ON THE INTERCONVERSION ENERGY BARRIERS OBTAINED FOR ATROPISOMERS OF SOME POLYCHLORINATED-BIPHENYLS BY AM1 SEMIEMPIRICAL QUANTUM-CHEMISTRY METHOD AND GAS-CHROMATOGRAPHY ON A MODIFIED CYCLODEXTRIN STATIONARY-PHASE

The interconversion energy barriers and dipole moments of atropisomers of four polychlorinated biphenyls (PCB 91, PCB 95, PCB 132 and PCB 13 6) have been calculated with AM1 semiempirical quantum chemistry metho d. The rest of all molecular parameters were optimized prior to each e nergy and dipole moment calculations. The interconversion energy barri ers found for some PCB by AM1 method, however, are substantially lower than those calculated from gas chromatographic data. This difference is proportional to intermolecular interactions of PCB atropisomers wit h a modified cyclodextrin stationary phase.